Limonis Cortex. U. S., Br. Lemon Peel. Limon. Cort.
"The outer rind of the fresh ripe fruit of Citrus medica Limonum (Risso) Hooker filius (Fam. Rutaceae)." U. S. "Lemon Peel is the fresh outer part of the pericarp of the fruit of Citrus medica, Linn., var. ß Limonum, Hook. f." Br.
Limonis Pericarpium; Ecorce (Zeste) de Citron, de Limon, Fr. Cod.; Cortex Citri Fructus, P. G; Citronenachale, Limon-enachale G.; Scorza di Limone, It.
For some general remarks on the genus Citrus, see Aurantii Cortex.
Citrus medica, or lemon tree, closely resembles Citrus Aurantium, before described. The leaves, however, are larger, slightly indented at the edges, and stand upon footstalks which are destitute of the winged appendages that characterize the other species. The flowers, moreover, have a purplish tinge on their outer surface, and the fruit is different in appearance from the orange. There are several varieties of Citrus medica, which some botanists consider as distinct species, but which scarcely differ except in the character of their fruits. Those particularly deserving of notice are the citron, lemon, and lime.
1. In the citron, C. medica genuina (Bentley & Trimen, p. 53), the fruit is very large, sometimes six inches in length, ovoid, with a double rind, of which the outer layer is yellowish, thin, unequal, rugged, with innumerable vesicles tilled with essential oil; the inner is white, very thick and spongy. It is divided in the interior into nine or ten loculi, filled with small oblong vesicles, which contain an acid juice precisely like that of the lemon, and used for the same purposes. The rind is applied to the preparation of conserves, to which it is adapted by its thickness. The fruit i.s called cedrat by the French.
2. The lemon, C. medico, var. Limonum (Citrus Limonum of Bisso) (Bentley & Trimen, p. 54) is smaller than the preceding, with a smoother and thinner rind, a pointed nipple-shaped summit, and a very juicy, acid pulp. In other respects it closely resembles the citron, to which, however, it is usually preferred in consequence of the greater abundance of its juice.
3. The lime is still smaller than the lemon, with a smoother and thinner rind, oval, rounded at the extremities, of a pale-yellow or greenish-yellow color, and abounding in a very acid juice, which renders it highly useful for the purposes to which the lemon is applied. It is the product of C. medica acida. According to E. M. Holmes the West India limes are much richer in acid than are those produced in the South of Europe; the juice of the spineless variety was found to contain 37.73 grains per ounce; the ordinary West India lime 36.15 grains per ounce; the Sicily lime 30.32 grains per ounce. Lime juice is recognized by the N. F. IV under the name Succus Citri.
The Citrus medica, like the orange-tree, is a native of Asia. It is now known to grow wild in Northern India, and was introduced into Europe from Persia or Media. It was first cultivated in Greece, afterwards in Italy, as early as the second century, and has now spread over the whole civilized world, being raised by artificial heat where the climate is too cold to admit of its exposure during winter to the open air.
Properties.—The exterior rind of the lemon has a fragrant odor, and a warm, aromatic bitter taste, somewhat similar to that of the orange, though less agreeable. It is usually found in narrow, thin bands, with very little of the spongy, white, inner layer adhering to it, and is officially described as follows: "The outer, lemon-yellow or dark yellow layer, recently separated by grating or paring and consisting of an epidermal layer, numerous parenchyma cells containing yellow chromoplastids, and large oil reservoirs' with globules of the volatile oil; odor highly fragrant, distinctive; taste pungent, aromatic. Under the microscope, sections of the rind, mounted in a fixed oil, show an epidermal layer composed of small tabular cells, a hypodermal layer containing numerous plastids, a mesocarp with colorless, thin-walled parenchyma and large, elliptical oil reservoirs; parenchyma cells containing a layer of granular protoplasm adhering to the walls and occasionally membrane crystals of calcium oxalate, which are irregularly polygonal in shape, and from 0.015 to 0.025 mm. in diameter." U. S.
"Outer surface pale yellow and more or less rough; with only a small amount of the white spongy part of the pericarp on the inner surface; in transverse section numerous large oil-glands below the epidermis. Strong, characteristic and fragrant odor; taste aromatic and bitter." Br.
It contains a bitter principle, and yields, by expression or distillation, an essential oil, which is much used for its flavor. Both this and the rind itself are recognized in the Pharmacopoeias. (See Oleum Limonis.) When the white, spongy portion of the rind is boiled in water, and the decoction evaporated, crystals are deposited of a substance called hesperidin. This is a glucoside, and has the formula C22H26O12, and is decomposed by diluted acids into hesperetin, C16H14O6, and glucose, C6H12O6. It turns dingy black when gently warmed with alcoholic solution of ferric chloride. It is bitter, but as it is found most largely in. the spongy and comparatively tasteless part of the rind, it may be doubted whether it is entitled to be considered as the active bitter principle. (See A. J. P., xxvi, 553.) Lemon peel yields its virtues to water, wine, and alcohol. E. G. Clayton (An., xix, 134) calls attention to the distinction between lemon peel and orange peel when moistened by strong hydrochloric acid. Orange peel under these circumstances changes in color from a yellow to a rich dark green color, while lemon peel retains its hue or assumes a dingy yellowish-brown tint.
The German Pharmacopoeia under the title of Cortex Citri Fructus requires that the lemon peel be derived from the completely developed but not fully ripe fruits of Citrus medico, L.
Uses.—The rind of the lemon is sometimes used to qualify the taste and increase the power of stomachic infusions and tinctures.